-LRB- CNN -RRB- -- It 's a moment familiar to any regular air traveler .

A passenger 's photo shows oxygen masks hanging from the ceiling on Monday 's Continental Flight 128 .

The plane bucks up and down , lurches forward and back , or both . Sometimes overhead bins fly open . The squeamish gasp . Babies cry . Then , usually , it 's all over .

In-flight turbulence is often a mere inconvenience . But it 's also the leading cause of airline passenger injuries that are not associated with a fatal crash , experts say .

And , on rare occasions , it can be deadly .

In the case of Monday 's Continental Flight 128 , an unexpected blast of air led to much more than jangled nerves , bumps and bruises .

Turbulence struck the flight , from Rio de Janeiro , Brazil , to Houston , Texas , unexpectedly , injuring seven passengers badly enough to require hospitalization after the pilot diverted the flight to Miami , Florida .

Police said 26 passengers were injured , four seriously . Learn more about airline turbulence ''

Turbulence , according to the Federal Aviation Administration , is caused by a quick change in air movement . Jet streams , air shooting off of mountains , cold or warm weather fronts and thunderstorms can all cause changes in speed or direction .

The rapid shift in gravity force -- or G-force -- can cause a sensation not unlike being whipped around on a roller coaster . Most of the time , discomfort is the worst byproduct .

`` Normally , it 's an inconvenience , '' said Kevin Garrison , a retired Delta Air Lines pilot living in Lexington , Kentucky . `` Very rarely does it hurt passengers , which is odd because a lot of them do n't keep their seat belts on . ''

And wearing seat belts , aviation officials say , is the best way to stay safe .

`` In the event that something happens , '' said Les Dorr , a spokesman for the FAA , `` that 's the best advice that we or anyone else can give passengers . ''

Since 1980 , three people have been killed in turbulence-related accidents , according to the administration . At least two of those deaths involved passengers who reportedly were not wearing seat belts while the seat-belt sign was on .

There have been 234 turbulence-related accidents since 1980 , and 114 passengers were seriously injured in those accidents , the FAA reported .

Flight attendants have been hurt at a much higher rate . During that same time period , 184 attendants were seriously injured , despite their numbers being far smaller than the number of passengers .

`` The majority of injuries actually happen to flight attendants , '' Dorr said . `` They have to be up performing their tasks , even when the seat-belt light is on . ''

And while pilots are almost always strapped in with seat belts , even they are n't exempt .

`` I 've had a few bloodied heads -- when I hit my head on the overhead when the seat belt was a little loose , '' said Garrison , who flew for Delta for 27 years .

In Monday 's accident , passengers reported they were slammed into the Boeing 767 's ceiling -- some said two or more times -- when the plane dropped rapidly .

`` I saw people being thrown to the roof as if they were dolls , '' Fabio Ottolini , who was returning to Houston with his wife and daughter after visiting family in Brazil , told CNN affiliate KTRK-TV .

Passengers said most of those injured were not wearing seat belts .

Initial reports are that the Monday flight was hit by what 's called clear-air turbulence , or air pockets that hit without warning .

While pilots are always on the lookout for regular turbulence spots -- like mountain ranges and places where weather fronts are converging -- clear-air turbulence can happen anywhere .

`` You ca n't see it ; you ca n't sense it with radar , '' Dorr said . `` The best way to determine if there 's a possibility of clear-air turbulence is to have somebody in front of you that 's already flown through it . ''

Dorr said passenger injury numbers have dropped over the past few years , during an industry-wide effort to increase safety .

No passengers were reported seriously injured in turbulence incidents in 2008 , and five flight attendants -- down from a high of 19 in 2003 -- received serious injuries , according to the FAA .

The Commercial Aviation Safety Team has focused on seat-belt awareness and pushed for better communication systems for reporting turbulence , Dorr said .

All licensed pilots also receive `` upset training , '' which teaches how to deal with extreme turbulence , he said .

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Three turbulence-related deaths since 1980 , FAA says

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At least two of the three were people not wearing seat belts

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Turbulence is caused by quick changes in air movement

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Air pockets from `` clear-air '' turbulence are hard to detect